Hard sintered composition

ABSTRACT

THE ADDITION OF UP TO 5 WT. PERCENT ZIRCONIUM CARBIDE TO HARD SINTERED COMPOSITIONS, FORMED OF TITANIUM CARBIDE, TUNGSTEN CARBIDE AND 10 TO 50% OF BINDING ALLOYS CONTAINING MOLYBDENUM AND IRON, COBALT OR NICKEL, TO BE USED IN CUTTING TOOLS FOR MACHINING METALS REDUCES CRATERING AND PLOWING WHEN MACHINING METALS AT HIGH SPEEDS.

HARD SINTERED COMPOSITION Filed Feb. 28, 1972 (Kg/mm TRANSVERSE RUPTURE STRENGTH ZrC (WEIGHT United States Patent Oflice Patented July 17, 1973 3,746,517 HARD SINTERED COMPOSITION Susumu Yamaya, Tokyo, and Takeshl Sadahiro, Yokohama, Japan, assiguors to Toshiba Tungaloy Co., Ltd., Tsukagoshi, Kawasaki-shi, Japan Filed Feb. 28, 1972, Ser. No. 229,960 Claims priority, application Japan, Dec. 23, 1971, 46 104 193 int. Cl. nzzr 1/00 US. Cl. 29182.7 4 Claims ABSTRACT OF THE DISCLOSURE The addition of up to 5 wt. percent zirconium carbide to hard sintered compositions, formed of titanium carbide, tungsten carbide and to 50% of binding alloys containing molybdenum and iron, cobalt or nickel, to be used in cutting tools for machining metals reduces cratering and plowing when machining metals at high speeds.

This invention relates to hard sintered compositions which are particularly highly resistant to cratering and plowing in machining metals at high speeds.

The hard sintered compositions, the chief ingredient of which is titanium carbide, have been widely used. These previous compositions are highly resistant to crateriug, but are poorly resistant to plowing as employed for cutting bits, which is the important field of the application of the compositions.

It is the object of this invention to provide the hard sintered composition improved with respect to the defect of the previous compositions.

According to the present invention, there are provided hard sintered compositions consisting essentially of (i) 5% maximum by weight of at least one metal carbide selected from the group consisting of zirconium carbide and vanadium carbide; (ii) maximum by weight of tungsten carbide; (iii) 10 to 50% by weight of binding alloys comprising to 70% by weight based on the binding alloy of at least one material selected from the group consisting of molybdenum and molybdenum carbide, and 75 to by weight based on the binding alloy of at least one metal selected from the group consisting of iron, cobalt and nickel; and (iv) the balance of titanium carbide. Titanium carbide can be substituted by tantalum carbide to the extent that the amount of the tantalum carbide weighs less than that of the titanium carbide.

The appended drawing depicts relationships between the amount of ZrC and the transverse rupture strength of sintered compact containing ZrC.

An example of the methods of manufacturing the compositions of this invention is explained as follows.

A titanium carbide powder and tungsten carbide powder substantially free of oxides and nitrides were chosen. The binding alloy powder was prepared by milling fifty percent of approximately five microns nickel powder and fifty percent of approximately one micron molybdenum powder. Together with these binding alloy powders, titanium carbide powder and tungsten carbide powder, there were mixed minus 325 mesh powderous materials such as zirconium carbide, vanadium carbide, cobalt, iron or tantalum carbide to manufacture various compositions as shown in the Table I, wherein compositions of this invention are indicated as A, B, C, D, E, F, G and H and the compositions I and J are also shown for a comparison purpose. These compositions refer to the compositions of the compact prior to reaction which may occur during sintering.

TA 13 LE 1 TiC Ni Mo Co WC ZrC VC TnC The compositions of this invention:

A 55 17 17 1 9 1 52 l0 l0 5 7 1 15 58 16 16 1 8 l 49 15 15 1 9 l 10 47 l6 l6 1 9 1 10 52 14 14 1 8 1 10 52 1D 10 5 7 15 H 58 16 16 1 8 0. 5 0. 6 The compositions for comparison:

The milling operations were conducted in a stainless steel mill containing cemented tungsten carbide balls, acetone being added to inhibit oxidation of the charge during the one hundred twenty hour milling period. After milling, the acetone was evaporated and four percent wax binder dissolved in benzene was added to the compositions. Upon drying, each of the powderous mixtures was pressed in a steel die at a pressure of about 1.5 tons/cm.

The cold pressed compacts were presintered in a hydrogen furnace at 650 centigrade for one hour to dewax the specimens. Final sintering was performed on an inert stool and in an inert ambient at 1350 centigrade for one hour in an induction furnace. An absolute pressure of about 0.1 to 0.3 micron was maintained in the furnace. The final sintering may be conducted in any suitable inert ambient, e.g. in an atmosphere of dry hydrogen, argon 0r helium. The period of sintering time depends on the sintering temperature. As the temperature is raised the sintering period may be shortened. In any event however the sintering temperature should not exceed 1480 centigrade in order to avoid substantial grain growth. The time and temperature of sintering must be adjusted so that the grain size of titanium carbide in the finished article is not substantially larger than that of the starting powder.

Table 2 shows the properties and cutting performances of the compositions shown in the Table 1. The hardness presents the Rockwell A hardness. and the unit of the transverse rupture strength is a kilogram per square millimeter. The width of plowing, presented by the unit of millimeter, was obtained by cutting a rod of HS S55C steel at a Brinell hardness of 303 using cutting fluid with a feed of 0.1 millimeter per revolution and a depth of cut of 1.0 millimeter at a surface speed of 30 meters per minute for one minute. The cutting conditions as described above are generally severe for a cutting bit, and render the bit subject to cratering and plowing at low speeds.

TABLE 2 Transverse rupture Width of Hardness strength plowing 90. 8 163 0. 35 92. 0 143 t]. 40 91. 0 0. 3T 91. 8 0. 37 91. 5 0. 32 92. 3 140 0. 44 92. D 148 O. 42 92. 3 140 0. 39 90. 9 142 0. 49 92. 0 0. 51

of nine percent of tungsten carbide, fifty percent of titanium carbide, fifteen percent of nickel, one percent of cobalt, fifteen percent of molybdenum, and ten percent of tantalum carbide. As shown in the drawing, when the amount of zirconium carbide exceeds five percent, the depression of the transverse rupture strength, namely that of the toughness of the compositions is remarkable. When zirconium carbide was replaced partly or wholly by vanadium carbide, approximately the same effect resulted. Therefore, the sum of zirconium carbide and vanadium carbide of the compositions of this invention should not exceed five percent.

It is essential that the binding alloy contain twenty-five percent to seventy percent of molybdenum and/or molybdenum carbide to take advantage of the ability of these materials to cause alloys containing them to wet the surface of the hard titanium carbide particles. The deficiency of the amount of molybdenum and molybdenum carbide makes said advantage insufiicient, and the excess of them depresses the toughness of the composition. Molybdenum carbide may be applied in the state of a solid solution with titanium carbide before sintering.

Among the iron group metals, nickel is preferred as a component of the binding alloy. However, any iron group metals or their alloys, may be employed. It is essential that the compositions contain ten percent to fifty percent of the binding alloy. The deficiency of the amount of the binding alloy depresses the toughness of the composition, and the excess of that depresses the hardness of the composition.

It is possible to substitute tantalum carbide for titanium carbide to the extent that the amount of titanium carbide weighs always more than tantalum carbide. The excess of tantalum carbide depresses the faculty of the composition for cutting bits. Tantalum carbide may take a form of solid solution with titanium carbide before sintering.

It is, of course, essential that all of the steps in the production of the finished tool be carried out so that the final product is free of detrimental amounts of oxides and nitrides.

It is essential that the composition contain fifteen percent maximum of tungsten carbide to take advantage of the ability of tungsten carbide to make the composition containing it highly resistant to the plastic deformation. The excess of the amount of tungsten carbide depresses the strength of the composition.

What we claim is:

1. Hard sintered compositions for use in cutting tools ti; machine metals at high speeds consisting essentially o (i) at least some zirconium carbide up to 5% maximum by weight,

(ii) at least some tungsten carbide up to 15% maximum by weight,

(iii) 10 to by weight of binding alloy which comprises,

(a) 25 to by weight based on the binding alloy of at least one material selected from the group consisting of molybdenum and molybdenum carbide and,

(b) to 30% by weight based on the binding alloy of at least one metal selected from the group consisting of iron, cobalt and nickel, and

(iv) the balance titanium carbide.

2. Hard sintered compositions according to claim 1 wherein the titanium carbide is replaced by tantalum carbide to the extent that the amount of the tantalum carbide weighs less than that of the titanium carbide.

3. Hard sintered compositions according to claim 1 wherein zirconium carbide is partially replaced by vanadium carbide.

4. Hard sintered compositions according to claim 1 containing about 1% by weight of zirconium carbide.

References Cited UNITED STATES PATENTS 3,490,901 1/1970 Hachisuka 75203 3,147,542 9/1964 Boeckeler 29182.7

2,711,009 6/1955 Redmond et al. 75-203 FOREIGN PATENTS 4,321,879 9/1968 Japan 29--l82.7

1,137,226 9/1962 Germany 29-182.7

CARL D. QUARFORTH, Primary Examiner B. HUNT, Assistant Examiner US. Cl. X.R. 75-203 

